To build on what [MENTION=930]dyn085[/MENTION] said...
Get an AccessPort from a tuner (Stratified, Mountune, Freektune, Tune Plus, whatever) and ask for a discount, because they might give you one. Worst they can say is no. You can also wait for a holiday sale or coupon to show up. They are frequent. Almost every tuner offers a free custom tune with purchase. You get the Cobb maps for free with this. This is the most important mod. Everything else is useless without it except the intercooler. ($450 - $500)
But a quality intercooler. I have the MTC intercooler myself. It's about $350 shipped from some dude on eBay. Other options that are good are the Deadhook and Map coolers. ($350 - $500)
Total cost of about $1000 factoring in shipping and taxes.
Research the shit out of and buy some good tires after this, maybe an RMM, and then get busy on shifter mods IMO.
You don't "need" anything else other than the two I suggested. You will achieve about 95% of what everyone else with all those nice noisemaker mods can make and spend a fraction of the cost doing it. After the AP/ tune and intercooler everything starts to become a VERY diminished return on investment.